Cathodic coupling oscillator for electronic music instruments



July 31, 1951 G. JENNY CATHODIC COUPLING OSCILLATOR FOR ELECTRONIC MUSICINSTRUMENTS Filed May 25, 1947 Patented July 31, 1951 OFFICE cA'rHonIoCOUPLING OSCILLATOR FOR ELECTRONIC MUSIC INSTRUMENTS Georges Jenny,Paris, France Application May 23, 1947, Serial No. 750,000 In FranceMarch 17, 1941 Section 1, Public Law 690, August 8, 1946 Patent expiresMarch 1'7, 1961 My invention relates to the generation of une dampedaudio frequency oscillations in electronic musical instruments.

It is an object of the present invention to provide an oscillatingsystem of high stability,

,It is a further object of my invention to. provide oscillations whichcontain a large amount of harmonics.

. Another object of the present invention is the provision of simple andeffective tuning and operating mechanisms for controlling the. pitch pfeach tone as well as for shifting the tone range covered by theinstrument.

Still another object is the separate and independent control offrequency intervals in response to the operating mechanism and thefrequency range covered by the instrument.

It is a still further object of my invention to provide an adjustablecapacitive-resistive oscillator output coupling impedance.

The electronic musical instrument according to this invention comprisesan electron tube system for generating audio oscillations. In thissystem two triodes, which may be contained in the same envelope, havetheir cathodes electrically connected, the grid of one triode beingconnected to the anode of the other triode. The grid of one triode isgrounded through a variable resistor, while the grid of the other triodeis connected to ground in any conventional manner.

The variable resistor inserted between the one grid and ground may becontrolled, for instance, by the operation of a keyboard or by means ofa metallic cord or band, grounded at one end. Provisions for alternativecontrol may be made.

Tunable capacitors may be used for tuning the oscillating system.

Further I propose to insert a resistive-capacitive impedance between thetunable oscillator and the subsequent audio frequency amplifier. Thisimpedance is constituted by an asbestos armature and a metal armatureadapted to contact and to compress the asbestos, whereby the impedanceof the asbestos, which is a function of pressure, is varied.

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specificembodiments when read in connection with the accompanying drawings, inwhich:

7 Fig. 1 is a wiring diagram illustrating acath- '1 Claims. (Cl. 84-420)odic coupling oscillator according to my invention;

Figs. 2 and 3 show two embodiments, respectively, of the keyboard andassociated elements.

As shown in Fig. 1, I'preferably use a double triode, 6 C8. The twocathodes Cl and C2 of this double triode are interconnected, andgrounded through a biasing resistance R C. The grid G2 is eithergrounded, as shown in Fig. l, or connected to ground by a resistance ofsmall value. A variable tuning resistance R GI between the grid Gl andthe ground is inserted. GI is connected to anode A2 through anadjustable capacity C V. The anode Al and the anode A2 are connected tothe voltage source, respectively, through the load resistances RAI andHA2. The connection between this oscillating system and a low frequencyamplifier of any type adapted to amplify and transform the electricoscillations into acoustic vibrations is established by a specialresistive-capacitive impedance constituted by an asbestos armature C anda metal armature D adapted to be moved toward one another forcontacting, these armatures being inserted between either anode A2 or Aland the input grid of the subsequent amplifier P. U. (Fig. 1).

The above-described connections produce undamped oscillations at audiofrequency as required in electronic musical instruments. Modi-:tications may be introduced, for instance by the incorporation ofcapacities in parallel with R C or the incorporation between G2 andground of a variable resistance. Instead of a double triode, I may usetwo separate triodes, two pentodes or similar tubes, the main feature ofthe oscillating system being in all cases the cathodic coupling obtainedthrough the electric connection between the two cathodes Cl and C2. Theonset of the oscillations is obtained through this coupling which may beeffected either through a direct connection between Cl and C2 or bymeans of a resistance or induction coil. The auxiliary featuresillustrated in the wiring diagram of Fig. 1 are the omission of theconventional induction coil which is a generalfeature in the oscillatingsystems now in use; furthermore one of the grid electrodes G2 isgrounded. It will be understood that additional induction coils,capacities or resistances may be added at different points as disclosedhereinabove without changing substantially the circuit shown in Fig. l.The electronic musical instruments schematically illustrated in Fig. 1,permits various different modifications and. embodiments which, due tothe cathodic coupling all have the following performance teatures:

(a) excellent frequency stability;

(b) a, basic sound extremely rich in harmonics thus allowing a largevariety of tones to be obtained by subsequent filtering;

(c) for a given value or C V (Fig. 1) it is possible, through variationof R, GI, to obtain a con tinuous variation in frequency between beatsand the upper limit or the sharpest audible sounds and even beyond.Conversely, for a given value of R GI, I obtain the same range through avariation of C V;

(d) the frequency shift obtained through an adjustment of the variableresistance R GI is not affected, when the frequency range is raised orlowered by an adjustment of C V. Similarly, the frequenc shiftassociated with shunting of C V by condensers 0 VI, O VII, etc., willnot be affected by a variation of R GI which modifies the frequencyrange covered.

These advantages are used together or sepa rately in the apparatus to bedescribed hereinafter. Iowever, other form of instrument incorporatingthese rticular means for modifying sound disclosed hereinabove failswithin the scope of the present invention.

In a first embodiment, 2, I have illustrated a piano keyboard of threeor four octaves. In this case R GI constituted. by a long graphiteresistance provided with movable collars. Each collar is connected tocontact d actuated by a keyboard key. When a key depressed, the point onthe resistance to which the associated collar is secured is groundedthrough the closing of the contact. The collars correspond to one halltone intervals of the nnisical scale, and the preliminary tuning of eachhalf tone is accomplished by displacing the collar in either directionalong the resistance. The general tuning, i. e. the displacement of allnotes on the instrument by one quarter of a tone, one half tone or onethird higher is obtained by operation or" the adjustable condenser C V.Additional shunting condensers such as C VI, C V2 allow an immediatetransposition one; two, three or more octaves higher. In practice, theapparatus covers 7 or 8 octaves with a keyboard of three octaves. Thevibrato is obtained by acting on C V or on R Al or on R A2.

In a second embodiment relating to a small accordion keyboard, eachkeyboard key controls the shunt insertion oi F3)? all adjustablecondensers such as (3 VI, C V2, tuning by semi-tones. The keyboardsystem is carried by a movable board. adapted to rotate round an axisand allowing a displacement of the keyboard to the right or to the left.This lateral displacement operates the variable resistance E (ii.Consequently slid-- ing during the playing possible, which is similar tochanges in position on the violin. The same may be the case forproducing a vibrato.

In a third. embodiment, Fig. 3, corresponding to an electronicclavichord associating strings with a keyboard, I associate a keyboardof the type i1- iustrated in Fig. with. a grounded metal string or stripA E stretched above the resistance R GI which may be coiled. It ispossible to play either on the keyboard or by pressing with the fingeron point of the string B to contact the resistance R GI, therebygrounding the resistance R GI at the point of contact. When depressed,the string A B will assume the position indicated by the dotted line inBy sliding the pressing finger along the string, I obtain a glissando 4in a manner similar to the playing of the violin. Thus the sameresistance R GI may be controlled by either the keyboard or the string.The instrument is tuned through operation of variable condensers, suchas C V, C VI, C V2.

What I claim as new and desire to secure by Letters Patent is:

1. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system including afirst and a second triode element each includin a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;and a condenser connecting the grid of said second element to the anodeof said first element.

2. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system including afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;a condenser connecting the grid of said second element to the anode ofsaid first element; a direct current source; and two resistancesconnecting, respectively, the anodes of said first and said secondelement to the positive terminal of said direct current source.

3. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system includin afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;an asbestos resistance; and an amplifier connected by said asbestosresistance to the output of said vacuum tube system.

4. In an electronic music instrument in combination, an oscillatorvacuum tube system tuned to audio frequency; said system including afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;a keyboard including keys corresponding to semitone intervals; means forvarying said resistance by the depression of said keys; and anadjustable condenser adapted to cooperate with said vacuum tube systemfor tuning the instrument.

5. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system includin afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;a keyboard including keys corresponding to semitone intervals; means forvarying said resistance by the depression of said keys; an adjustablecondenser adapted to cooperate with said vacuum tube system for tuningthe instruments; and a plurality of condensers adapted to be connectedin parallel to said adjustable condenser for transposing the tuning.

6. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system including afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalcon nection between the grid of said first element and ground; avariable resistance connected between the grid of said second elementand ground; a keyboard including keys adapted to control the variationof said resistance; and a grounded string adapted to contact saidresistance whereby the pressure of the finger of the player on saidstring grounds said resistance at the point at which the finger acts.

7. In an electronic music instrument in combination, an oscillatoryvacuum tube system tuned to audio frequency; said system including afirst and a second triode element each including a cathode, a grid, andan anode; an electrical connection between said cathodes; an electricalconnection between the grid of said first element and ground; a variableresistance connected between the grid of said second element and ground;an

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 2,070,344 Waters Feb. 9, 19372,276,389 Hammond Mar. 17, 1942 2,300,632 Pooh Nov. 3, 1942 2,307,375Blumlein et a1. Jan. 5, 1943 2,383,822 Schlesinger Aug. 28, 19452,396,224 Artzt Mar. 12, 1946 2,416,201 Nagel et a1 Feb. 18, 1947

